WEST NILE VIRUS

Background Information

What is West Nile virus?
The West Nile virus is a mosquito-borne virus that can cause mild symptoms or occasionally a more serious illness. Although the chances of a person getting sick are small, there are some simple steps you can take to reduce your risk of being bitten by mosquitoes, such as covering up and using an insect repellent.

How do people become infected with West Nile virus?
People become infected with West Nile virus primarily through the bite of a mosquito that carries the virus. Mosquitoes become infected with West Nile virus when they feed on the blood of infected birds. These infected mosquitoes can then transmit West Nile virus to humans and to other birds. West Nile virus is not known to be spread by birds or other animals to people or by direct person-to-person contact.

What is the risk for becoming ill?
Everyone who is active and outside during the summer months is at risk from West Nile virus and should take precautions to avoid mosquito bites.

Of the dozens of species of mosquitoes found here in Ontario, only a small percentage carry the West Nile virus. The most common is Culex pipiens (nicknamed the rain barrel mosquito), which lives near humans, much like the common housefly. Scientific research indicates that four out of five people bitten by a mosquito infected with West Nile virus do not show any symptoms of the illness.

The risk of being bitten by an infected mosquito depends on how many of the small number of mosquito species that actually carry the virus are present in a specific area.

What effect does West Nile virus have on people?
Only a small percentage of bites from an infected mosquito may lead to West Nile virus infection and, in turn, mild or serious illness.

Most people who become infected will experience no symptoms or have very mild illness. For some, the symptoms will be more pronounced including high fever with muscle weakness, stiff neck, confusion and a severe headache. For a very rare few, the virus causes serious neurological illness. Symptoms generally occur from 5 to 15 days after exposure. For more information, consult your physician.

Can you get West Nile virus from other insects, such as ticks?
At present, scientific research indicates that West Nile virus is only spread to humans through a bite from an infected mosquito.

 

 

 

Last Modified: May 7, 2003
Queen's Printer for Ontario, 2007